1. Field of the Invention
The present invention relates to an ink jet recording medium having a plain-paper-like feel, on the surface of which an ink receiving layer has been formed, and an ink jet recording method in which an image is formed on this ink jet recording medium with a water-based ink.
2. Related Background Art
Ink jet printers according to an ink jet recording system have been recently spread because a wide variety of printed images such as multi-color and high-quality photograph images, art images, poster images, office documents and CAD images are easily obtained at high speed from an ink jet printer.
Inks for this ink jet printer include water-based dye inks and water-based pigment inks. Accordingly, the printers include printers with which printing is performed with only water-based dye inks, printers with which printing is performed with only water-based pigment inks and printers with which printing is performed by using water-based dye inks and water-based pigment inks in combination.
Printing is very often conducted on plain paper, which is a medium of lowest prices, using such an ink jet printer, and so plain paper having high performance in spite of low price is required. However, plain paper, which can provide a printed article of sufficiently high performance, i.e., can achieve high coloring comparable with the so-called matte coated paper, even when printing is conducted with either a water-based dye ink or a water-based pigment ink, has not been yet realized under the circumstances.
The reason for this is considered to be as follows. The surface structure of ordinary plain paper is mainly formed of pulp fibers. When a water-based dye ink is used, an adsorption site of a dye is limited to the surfaces of the pulp fibers, and the adsorption site is small compared with matte coated paper, the surface of which is covered with inorganic fine particles. Therefore, the colorability is limited. On the other hand, when a water-based pigment ink is used, pigment particles fall in interstices between the pulp fibers, so that the amount of the water-based pigment ink fixable to the vicinity of the surface of the ink jet recording medium (plain paper) is limited, and so high coloring is not achieved.
In order to solve such problems, it has heretofore been attempted to improve fixability of water-based dye inks and water-based pigment inks. For example, an ink jet recording medium obtained by coating the surfaces of pulp fibers or the interiors of the pulp fibers with a cationic resin or polyvalent metal as an ink-fixing agent has been proposed (see Japanese Patent Application Laid-Open No. S61-058788). In this ink jet recording medium, the ink fixability is improved by an ionic action between the cationic resin or polyvalent metal ion and an anionic ink. In the case of the water-based dye ink, a large amount of the ink is fixed to pulp fibers existing in the vicinity of the surface of the ink jet recording medium. In the case of the water-based pigment ink, pigment particles are aggregated not only on the pulp fibers of the ink jet recording medium, but also in the interstices between the pulp fibers. It is said that the ink can be thereby fixed as near to the surface of the ink jet recording medium as possible. However, according to this method, the colorability is not sufficient, and colorability of the level of the matte coated paper has not been yet achieved.
As another ink jet recording medium than the above-described recording medium, there is also one obtained by coating the surfaces of pulp fibers with a water-soluble resin and a swellable resin as an ink-fixing agent and an ink-receiving agent. However, even by this method, interstices are left between pulp fibers after all, and thus the ink adsorption site thereof is limited, so that colorability has not been sufficient. In addition, this recording medium has involved a problem that the ink absorption capacity of the resulting ink receiving layer is small, and the absorption rate becomes low.
An ink jet recording medium obtained by forming silica on a substrate of pulp fibers and fixing pigment particles on to the silica has also been proposed (see Japanese Patent Application Laid-Open Nos. H04-298378 and 2003-276319). In this ink jet recording medium, when a water-based dye ink is used, the water-based dye ink is fixed to the silica, and so good colorability is achieved. However, the ink jet recording medium prepared by this technique has have a surface texture different from a feel of pulp like plain paper, and the surface texture thereof has been a feel like the so-called matte coated paper. The reason for this is that it is generally necessary to apply the silica to an ink receiving layer in a large amount of about 5 to 30 g/m2.
Further, an ink jet recording medium obtained by controlling the amount of silica applied to an ink receiving layer to 1 to 3 g/m2 smaller than the amount conventionally used and controlling the secondary particle size of the silica to from 3 μm or more and 30 μm or less has been proposed (see Japanese Patent Application Laid-Open No. 2002-046343). However, this recording medium does not have such a specific pore size region as shown in the present invention and fails to achieve colorability of the level of the matte coated paper for the water-based dye and pigment inks in spite of a feel like the plain paper.
Still further, an ink jet recording medium obtained by forming a thin layer of inorganic fine particles having a very fine particle size, such as alumina or dry silica, on a substrate of pulp fibers has been proposed (see Japanese Patent Application Laid-Open No. H09-095044). However, these inorganic fine particles are those used in the so-called glossy paper, and so a desired plain-paper-like feel is not obtained because glossiness develops on the surface of the resulting ink jet recording medium. In addition, a problem that the material cost is high has also been involved.
Yet still further, ink jet recording media for which ink-absorbing capacity and print density have been improved by controlling a pore volume of a specific pore size region formed in an ink receiving layer have been proposed (see Japanese Patent Application Laid-Open Nos. H10-324058 and H05-246131). However, these ink jet recording media have not been such that silica is applied in such a small amount (from 0.2 g/m2 or more and 2.0 g/m2 or less in terms of solid content mass) that a plain-paper-like feel can be realized. In addition, these recording media do not have such both pore size regions of a specific pore size region to be an adsorption site most suitable for water-based dye inks and a specific pore size region to be an adsorption site most suitable for water-based pigment inks, as shown in the present invention. From this reason, the recording media have failed to achieve colorability of the level of the matte coated paper for the water-based dye and pigment inks in spite of a feel like the plain paper.
In order to obtain a wide color reproduction range, it has been necessary to use a large amount of an ink in the conventional ink jet recording media. However, the use of the large amount of the ink has involved problems that it takes a long time for drying because a substrate (pulp fibers) absorbs water, and that cockling (waving) or curling occurs. In order to provide a printed article at low cost, also, it is better to lessen the amount of the ink required of the formation of an image, and so an ink jet recording medium capable of achieving high coloring by a small amount of an ink has been required. However, the ink jet recording medium capable of achieving high coloring by a small amount of an ink has not been yet realized.